On the search for limiting forces in normal sections of reinforced concrete elements when calculating using a nonlinear deformation model

Abstract

Introduction  . The article analyses the stress-strain states of reinforced concrete elements when calculating the strength of normal sections using a nonlinear deformation model NDM, proposes a method for describing axial deformations and forced in the form of function parameters, introduces criteria for grouping deformed states based on emerging forces. An analytical method is proposed for determining the limiting forces in the normal section of a reinforced concrete element when calculating strength according to NDM. Aim.  Development of a methodology for finding the limiting forces at which there is no significant degradation of the rigidity of the normal section in a reinforced concrete element when calculating using the NDM, which does not require the use of numerical modeling tools. Results.  The results of the research showed that recording the deformed states of the section in the form of parameters of the axial deformation equation makes it possible to describe the mechanisms of NDM in the form of a system of nonlinear equations, which makes it possible to express direct analytical dependencies for finding deformations from forces. A group of stressstrain states of normal sections has been identified, which can be characterized, from the point of view of forces, as close to the maximum possible (about 90…100 % in bending moment), and from the point of view of rigidity as a boundary, after crossing which a sharp degradation of the rigidity characteristics of the section is observed. Analytical dependencies describing the identified group made it possible to abandon the use of numerical methods to determine limiting forces according to NDM. Conclusions. A method for determining the limiting forces in the normal section of reinforced concrete elements when calculating according to the NDM has been developed, which does not require the use of numerical models. The essence of the method lies in the established mutual dependencies between the parameters of equation of the deformed state of the section, at which forces close to maximum possible are observed in it, and there is no sharp degradation of the rigidity characteristics of the normal sections.